Chemical vapor deposition (CVD) processes are typically utilized in production of integrated electronic semiconductor components in which numerous layers of various types of materials are deposited one layer at a time onto a Silicon or other semiconductor substrate wafer. In a typical CVD manufacturing process, round wafers of extremely pure silicon, germanium or other semiconductor substrate typically of a diameter between 2 and 12 inches, comprise a base onto which layers of conducting, semi-conducting and insulating materials are successively deposited. Gates and paths as well as circuit elements are etched into each successive layer, usually by photolithic and laser illumination processes. In this way the layers are interconnected forming an integrated array of electronic processing devices and circuits. Several dozen to several hundred identical individual integrated circuits/devises are typically simultaneously deposited onto a single wafer at a time. The deposited base wafer is then cut up to into individual devices or "chips" either before or after they are electronically tested for defects. The individual chips are then incorporated into electronic devices, such as computer boards, toys, household electronics, automobile circuits, manufacturing equipment, commercial equipment, and the like.
The CVD process is typically described in terms of temperature-dependent phase change and nucleation/deposit phenomenon and typically involves reactions and commingling of one or two vapor phase fluids or gases in combination with a reactive surface. In many instances the source of the reactant gas is fluid in liquid phase which must be vaporized with minimum perturbation of vapor phase fluid pressure, temperature and volume parameters in the process or reaction vessel to achieve uniform, well formed layers of deposited materials. In other words, as in other precision manufacturing processes, limits and tolerances are narrow.
In the prior art, numerous designs for reaction chambers and parameters are described for achieving the rigorous operating conditions in chemical vapor deposition processes for depositing integrated semiconductor circuits. For example, U.S. Pat. No. 5,091,219 to Monkowski et al issued Feb. 25, 1992 describes a CVD process which requires specific geometries and flow patterns of the reactant gases within an essentially cylindrical reactor. This patent teaches that uniformity and control over layer deposition is accomplished by directing flow pattern of reactant gas through the reactor.
U.S. Pat. No. 5,098,741 to Nolet et al issued Mar. 24, 1992 teaches a method and system for delivering liquid reagents to processing vessels wherein a volume of liquid reagent is metered to an expansion valve with an adjustable orifice which increases and decrease in diameter responsive to up stream of the liquid pressure. The liquid reagent flashes to vapor phase as it passes through to the downstream side of the expansion valve which typically is at a much lower pressure. Energy (heat) is supplied to the downstream side of the expansion valve, i.e., a vaporization chamber or vaporizer located upstream from the reactor vessel to provide necessary heat of vaporization to prevent fogging and droplet formation. The point of the adjustable orifice in the expansion valve is to minimize perturbations in the pressure of vapor phase reagent (mass flow rate) downstream of expansion valve due to inert gases dissolved in the liquid reagent upstream from the expansion valve.
U.S. Pat. No. 5,320,680 to Learn et al issued Jun. 14, 1994 teaches a primary flow CVD apparatus comprising gas preheater and a geometry promoting substantially eddy-free gas flow. This patent attempts to describe an operative reaction chamber with a hot wall reaction tube, and primary and secondary reaction gas preheaters vessels each with gas injectors directing heated gas into an annular mixing zone immediately upstream of the cylindrical reaction tube. The idea is that the reactant gases are preheated as they are injected into the annular mixing zone which because of its coaxial relationship with the reaction tube promotes highly laminar reactant gas flow through the tube perpendicular to the edges of wafers stacked in boats within the reaction tube. Preheating immediately upstream of the reaction tube and laminar flow perpendicular to stacked wafer edges is thought to reduce wafer contamination due to premature nucleation (particle formation) of the reactant gases, eddies and stagnant regions within the reaction tube volume. Learn et al doesn't discuss problems associated with a liquid phase source for the primary or secondary reactant gases.
U.S. Pat. Nos. 5,361,800, 5,371,628 and 5,437,542 issued Nov. 8, Dec. 6, 1994 and Aug.1, 1995, respectively, to Ewing describe direct liquid injection positive displacement liquid pump and vaporizer systems. The automated valve pumping systems use a pair of pumps operating in opposition to provide continuous and constant volumetric flow of liquid to a vaporizer using a stack of disks heated for flashing the liquid reagent to vapor the liquid.
U.S. Pat. No. 5,421,895 to Tsubouchi issued Jun. 6, 1995 et al teaches an apparatus for generating and then vaporizing small droplets of liquid phase reactant comprising a piezoelectric vibrator vibrating an open nozzle tip for ejecting a liquid droplets at ambient pressure into small pores through a heated plate into a vapor chamber maintained at substantially lower pressure.
U.S. Pat. No. 5,510,146 to Miyasaka issued Apr. 23, 1996 teaches a CVD apparatus and method of fabricating a thin-film semiconductor device. This low-pressure system produces a thin film forming a channel portion inside a reaction chamber in which the pressure is reduced at a specified rate at the commencement of the procedure.
U.S. Pat. No. 5,620,524 to Fan et al issued Apr. 15, 1997 teaches a system based upon a continuous delivery, micro metering pump pumping a liquid phase reagent fluid to provide a continuous flow pulse-free vapor phase reagent flow manner depends on the capacity and restrictive connection of the pump to its external environment, as well as the electronic control circuitry and control algorithms used to control the motion of the displacement elements of the pump.
However, an alternative approach to achieving a uniform, controllable and effective layer deposition on a substrate is to utilize a liquid precursor system with feedback control based on the pressure and temperature of the vaporized precursor relative to an initial stage vaporizer. The prior art does not teach the use of a controller for a liquid shot pump which receives an operating signal from a pressure transducer measuring the pressure of a temperature controlled front end vaporizer.